The invention relates to a process regulating system as well as a method for carrying out the process.
It is known to utilize, in process regulation systems for ensuring the quality of resistance welding connections, a substitution variable as the command variable, since the parameter which is actually of interest, the spot diameter, cannot be monitored during the welding (Publication "Schweissen und Schneiden", Vol. 32, (1980), No. 12, pages 491 to 495).
A process is also known regulating spot welding (See German patent document DE-OS 37 11 771) in which the mechanical and/or electrical process parameters given for the welding process are monitored during welding and each change of the process parameter within the welding process is fine tunable via several manipulated variables. The welding area is, to this end, subdivided into several areas for regulation, wherein to each of these areas an evaluation scheme is assigned. The trace of the curve for different materials and dimensions is determined on the basis of actual structural parts and is stored.
If a mathematical-physical model of the process cannot be formulated, from which the command variables and other variables of the regulation system can be determined, often the only alternatives are to use either:
a process control in which the control parameters for achieving the target function are optimized and interference influences on the process are either prevented through suitable measures or are compensated for; or
a process regulation with a command variable which describes the target function only insufficiently and consequently can only conditionally compensate for interferences and erroneous process runs.
The invention provides a process, and a device for carrying it out, with which for example the special technical processes in which a functional connection between process input and output parameters parameters is at least in part unknown, while maintaining given limits on the characteristics of the output parameters (target function).
Characteristics of processes in which a functional connection between process input and output parameters is at least in part unknown, are that
in the process (for example in a machine or reactor) variable input parameters, i.e. which are changeable from the outside, are entered through which the process can be influenced,
interference parameters act upon the process whose occurrence and effects on the process are not predictable, and
the result of the process are one or several output parameters, which are to have particular previously defined properties.
In many cases the target function is a parameter which is not directly measurable so that it cannot be fed back to the process input--in the sense of a "classical" regulating circuit. On the other hand, a target function and measurable physical parameters, which may not necessarily be output parameters, often have no unique correlation so that the problem resides in defining one or several command variables for process regulation which permit a sufficiently accurate description of the state or the course of the process.
The starting point of the invention is the structure of a process regulation system with one or several manipulated variables and several command variables. The command variables are derived from the measurable process parameters. These derivations have the goal of reducing the information content of the measuring signals in the sense of a characteristic extraction.
The regulation takes place for each manipulated variable according to an estimated regulation rule.
Measured variables and the derivations herefrom (command variables) which are present as calculation rules, cannot be estimated and must be tailored to the particular type of process. Furthermore, it is assumed that the process is in principle repeatable or proceeds periodically and can be made discrete in time.
The conversion factor corresponds to the sensitivity of the system and must be adapted to the particular process. If the system with respect to different command variables reacts with different sensitivity, for each command variable a conversion factor can also be introduced.
In the method according to the invention the nominal values of the command variables and the normalized weighting factors are determined so that therewith, regulation can be carried out directly.
The process data (signal function) to be measured in real time are sensed and stored. Command functions whose progression in time is to describe the course of the process are calculated. These command functions result from the preprocessing of the signal function among which are counted also interlinking of several measured variables (for example: a command function "electrical resistance" in the quotient of signal functions "voltage" and "current"). The calculating rules for the individual command functions are a function of the type of process involved, and are defined by the user of the regulation system. The user can define any number of command functions. It is also possible to select command functions where a relationship with the target function is not expected a priori.
Based on a number of recorded process runs which can take place with an open (process control) or also a closed regulating circuit, an whose signal functions were recorded, command functions can be established and statistically evaluated. The command functions are sorted with respect to their ability for maintaining particular limits of the target function in terms of category according to the result of the process.
Within the scope of an analysis for each individual command function a mean value and an error function are calculated. The error function describes the reproducibility of the command function for different trials whose test results are classified identically. As a result of the analysis the following are available:
the mean value curves of a first category which are supplied directly as nominal values for the individual command variables to the regulation device,
the standard deviations of the mean value curves of a second category, and
the mean value curves of a third category which, if necessary, is subdivided.
From the mean value curves and their band spreads (standard deviations) the weighting functions for the individual command variables are calculated.
The weighting functions are normalized to values between +1 and -1. According to the normalization the value "0" signifies a place of the identification function which--with respect to the process result to be expected is not significant, while the values +1 and -1 make clear positions of highest significance (=correlation between command variable and target function).
The sign of the individual values of the weighting functions indicates the direction of change of the manipulated variable if a deviation has been detected.
The invention is advantageous in particular in that for a process regulation system with the stated boundary conditions, means are provided with which the regulation parameters, such as nominal-value functions and weighting factors, can be determined automatically and wherein diverse intervention options for user flexibility is largely maintained to make possible individual adaptation to different technical processes.
Sensors of the device according to the invention can be optical, chemical and/or electrical sensors for optical, electrical, mechanical or material properties such as concentration, density and the like.
Command variables for which over the entire process time only small weighting factors can be determined, are not suitable for process regulation. They must therefore be selected out. The limit for such a selection is based on whether or not other suitable command variables exist or whether in particular process stages, a regulation can be dispensed with.
Of importance is that in the estimated regulating rule or equation of the regulation device, the current values of the identification functions are entered as actual values, and that mean value functions are entered as nominal values. The difference between the values supplies the deviation for each command variable. Since the command variables in comparison with each other and as the related to the time during the process can be of different significance, the deviations are multiplied the associated weighting factors. The sum of the weighted deviations yields the total deviation which with the aid of a process-specific conversion factor, is brought into the order of magnitude of the manipulated variable.